Field of the Invention
The problem of seeking a parameter which indicates directly the quantity or mass ratios of substance pairs in multicomponent mixtures arises based on the realization that the ratio of the quantity of mass of one substance to the quantity of mass of a second substance, rather than the ratio of the quantity or mass of this substance to the quantity or mass of all substances contained in the mixed phase, is determining for chemical reactions and equilibria.
The quantity or mass ratio was formerly determined from the ratio of the contents or from the ratio of the concentrations of the two substances, depending on whether the parameter used depends on the mass, the quantity or the volume of the sample. A direct parameter of the mass or quantity ratio of two substances, i.e. one independent of mass, quantity and volume of the sample, was not known until a short while ago.
To determine the concentrations of the two substances, for example, on the basis of the substance dependence of the spectral intensity distribution of the radiation transmitted by the sample, one used to measure the radiation intensity or its first, second or a higher derivative at at least two different points of the spectrum.
For these two measurements, separated in space or time, it was necessary to measure or to maintain constant the sample quantity or the sample volume, the pressure and the temperature, and to eliminate disturbing components. These measures though necessary when using a parameter which depends on the absolute amount of the two substances, are not necessary when using a parameter which depends exclusively on their ratio.
In DT-OS 2,460,895 a measuring method was described for the first time which furnishes direct parameters for the quantity of mass ratio of two components of a mixed phase which correspond to the first and second difference .DELTA..sup.1 J/.DELTA..sup.2 J or respectively to the ratio of the first and second derivative J'/J" of the spectral intensity distribution. These parameters have the advantages that they reproduce with great accuracy especially the small deviations from that mixture ratio at which the first difference .DELTA..sup.1 J or respectively the first derivative J' is zero, and that they are independent of the absolute amounts of the substance quantities in the ray path and therefore are not adversely influenced either by dilution with other substances or by a variation of the pressure or the temperature, or by a variation of the intensity of the radiation source or by smoke and dust. However, the measurement range in which these advantages are effective is relatively small in this method.
In U.S. Pat. No. 2,834,246 an apparatus for the modulation of a measuring light ray by means of a rotating interference filter has been described. On the basis of this publication it was to be expected that one can adjust the mean value of the wavelength of the transmitted light by means of the angle which the axis of rotation forms with the perpendicular erected on the filter. Applicant's experiments with the known apparatus, however, could not clearly confirm this.